Abstract. This note provides a self-contained introduction to Rader's fast Fourier transform (FFT).We start by explaining the need for an additional type of FFT. The properties of the multiplicative group of the integers modulo a prime number are then developed and their relevance to the calculation of the discrete Fourier transform is explained. Rader's FFT is then derived, Rader's zero-padding technique is described, and the performance of the unpadded and the zero-padded approaches is examined. noting that each sum is now an I-term DFT that should require on the order of I 2 calculations, and noting that whenever you need terms that go past the "natural end" of a DFT you do not need to perform more calculations: instead, you find the additional terms by making use of the periodicity of the DFT. Calculating the DFT using this strategy takes on the order of I 2 L+(L−1)N operations, where the (L−1)N *